Enantiospezifische Synthese und Allylierung ausschließlich Kohlenstoff‐substituierter, α‐chiraler Allylstannane

Abstract

Endlich frei wurde der Weg zu den Titelverbindungen in nahezu enantiomerenreiner Form mit einem Bis(triorganostannyl)zinkreagens (siehe Schema). Diastereoselektive thermische (links) und Lewis‐Säure‐vermittelte Folgereaktionen (rechts) veranschaulichen das Synthesepotenzial dieser Verbindungen.

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“…[33,34] Initial screening showed that it was indeed possible to generate allylic stannanes 19-21 in near quantitative yields but their isolation and determination of their enantiomeric excesses by GLC or HPLC failed. [36] We therefore processed fragile 19-21 directly in thermal allylation reactions with benzaldehyde. [58] The corresponding homoallylic alcohols 22-24 were obtained in moderate yields, typical for this transformation.…”

“…With the chemistry of (R 3 Si) 2 Zn unexplored, we set out to examine the generation of (R 3 Si) 2 Zn32–34 and that of the related (R 3 Sn) 2 Zn35, 36 (Scheme ). For this, corresponding R 3 SiCl and R 3 SnCl are treated with lithium to form R 3 SiLi and R 3 SnLi,31 respectively.…”

“…We chose the same substrates as for the related carbonsilicon bond formation (Scheme ) 33. 34 Initial screening showed that it was indeed possible to generate allylic stannanes 19 – 21 in near quantitative yields but their isolation and determination of their enantiomeric excesses by GLC or HPLC failed 36. We therefore processed fragile 19 – 21 directly in thermal allylation reactions with benzaldehyde 58.…”